A chip may have different modes and configurations. For example one of the pins can be used either as output of linear regulator or as a DC-to-DC convertor coil pin. In the first case when it is configured to linear regulator the pin is connected to a capacitor. In the other case when it is configured to DC-to-DC, the pin is connected to a coil inductor or another electrical module that reacts to electrical current differently than a capacitor.
In order to detect the configuration of the chip, a strap may be used. A strap is a pin, which can be used in the startup for identifying a configuration or a mode of the chip according to their state, whether they are tied up or down. In some cases, there are no free pins for strapping since all the pins of the chip are occupied by other strap options or being used in power up of the chip.